What`s mean delay?

Hi. I want to know whats mean exactly delay. Its the time between the two programs or the time while is run one of them?
Sorry for my bad english.

It's the length of time the processor can do absolutely nothing except service interrupts.
We don't talk about delay() in polite company.

So, its a... pause? My program cant run in delay?

I don’t know what your program is.
It might run solely in interrupt context, but normally when the processor hits a “delay()”, it can do nothing else except service interrupts until the delay period has elapsed.

So, its a... pause? My program cant run in delay?

If your program has the line, for example delay(2000); the Arduino will do nothing until 2000 milliseconds have elapsed. Then it will go on with the next instruction.

The delay() function can be useful for small demonstration or test programs but you should not use it in any serious program because the Arduino can do nothing during the delay period. It is much better to use millis() to manage timing as illustrated in several things at a time.

To give a practical example, if you want to cook a chicken you do not sit watching the oven for 90 minutes (or whatever). You do other things - like watch golf on TV. When the cooking time is finished you take the chicken from the oven.